DESCRIPTION: (Applicant's Abstract) Acceptance and Commitment Therapy is grounded in the basic behavior analytic research on derived stimulus relations. This empirical and theoretical framework suggests that the attempt to avoid private experience (thoughts, feelings, memories, bodily sensations) is ubiquitous, and also may serve as a pathogenic process. Many psychological models of substance abuse suggest that substance abusers use, in part, to reduce (i.e., escape or avoid) stress or anxiety. The present proposal argues that the development and maintenance of abstinence may be more likely if emotional avoidance itself can be changed. Acceptance and Commitment Therapy (ACT) is designed to accomplish this goal. The objectives of the proposed research are to compare ACT to Twelve Step Facilitation in the development and maintenance of polysubstance-abusing methadone clients in a 24-week randomized clinical trial with a six month follow up. The specific aims are to generate sufficient data to provide a basis for a power analysis, to test the acceptability of ACT in the treatment of opiate dependent individuals, to make a preliminary evaluation of the durability of the treatment effects generated by ACT, to assess the reliability of our measures of treatment adherence and competence, to assess the relationship between treatment adherence and competence and client outcome, and to develop data on the active mechanism of change in ACT as a route to matching hypotheses to be tested in a subsequent study. The purpose of the present proposal is to increase knowledge on treatment for an extremely costly and difficult client population, whose multiple and chronic addictions have numerous related social and health costs.